Most scientists believe that the current global warming is caused by man-made emissions of greenhouse gases and that the most important of these gases is Carbon Dioxide or CO2.
They also believe that the Sun’s influence for this warming is very small. We now know that the irradiance or “heat transfer” from the Sun to the Earth has varied relative little during recent decades. Therefore the conclusion that most scientists have done is that the resent warming must be man-made, this is because they haven’t found any other reasonable explanation.
However what we know over how much a specific increase of CO2 has on global temperature is poor. The reason in that the knowledge of how greenhouse gases affect cloud formation is mostly down to speculations. Cloud formation physics is quite a complicated process to explain with many factors.
So, rather than having a solid theoretical and measured basis for how much man-made greenhouse gases affect the climate, the made estimation is mostly down to deduction.
They argue: We know how much the temperature has increased so therefore we can calculate how much a specific increase in greenhouse gases will increase the global temperature in the future. We have done this through deduction as we already have attributed the known increase to be greenhouse driven.
However scientists who study the Sun have long noted similarities between solar activity and terrestrial weather patterns.
Also the weather changes the last century is not something unique. Given the relative small changes in the observed irradiance “heat emitted from the Sun”, those changes in temperature during past centuries are hard to explain if you don’t include some other types of influence from the Sun.
It was not until the Danish scientist Henrik Svensmark suggested that cosmic radiation could influence cloud cover that a plausible explains for this apparent correlation was given.
Here is this theory!
When the Sun is very active, as it is now, the solar wind and the solar magnetic field are both strong. This in turn shields the Earth from high energy particles coming from the cosmos, usually from particles which were once created in supernova explosions. This affects low cloud cover formation as the radiation create ions which seeds cloud forming water droplets. During times when there are many high energy particles reaching low altitudes there are more low cloud cover and the Earth cools. When there are few high energy particles penetrating to low altitudes then less clouds form and the Earth warms.
Usually clouds higher up in the atmosphere are almost always ionized from both low and high energy particles because both those types of particles penetrate high altitudes at all time.
The created variations are only in the low altitude cloud cover which is affected by very high energy cosmic particles.
Recently an experiment called SKY (Cloud in Danish) was made by Svensmark which conclusively confirmed this cloud forming mechanism experimentally and that this type of cosmic ionization has an important seed effect on clouds. Links between low cloud cover variations and high energy particles intensity have also now been confirmed by satellite studies.